Be a Bonsai Sleuth: What is Needle Cast and What is Overwatering for Pines?

Many of the problems we see on our bonsai look very much the same. Needle Cast, a fungus, and overwatering, a care mistake, often look a lot alike. Here are two photos that might help determine if you have one or the other of them in your yard: This pine, a Ponderosa, has been overwatered. Notice the nearly equal lengths of browned tips. Whenever you see this, think, ‘This soil has stayed wet for too long.’ It may be because of water retentive soil, or perhaps it’s been watered too frequently. Adjusting the watering pattern for this tree, or changing its soil, should solve this problem in a year’s time. This Ponderosa Pine has Needle Cast, a fungus. Notice the discoloration, the uneven browning of the needles, and the the green/yellow/red banding, especially in the green parts of the needle. The treatment for this tree is spraying with Daconil or a copper fungicide when the new needles are coming out. In most areas this means spraying in the springtime (though in some unusual areas such as the Pacific Northwest of the United States it can also be late summer and fall). It will usually take a year or two of careful management to get beyond this problem, so have patience. Not that easy to tell apart, are they? And yet, identify which is which, apply the correction, and you’ll likely have success. Don’t identify it and you’ll likely have what history buffs know for certain…a repetition of the same thing…